Over the last few decades, many methods have been proposed to evaluate non-native leaners' pronunciation quality at the aforementioned levels. Most of these methods can be divided into two major groups, namely one-step or two-step approaches. Methods in the former group directly utilize confidence scores [1]}, [2]}, [3]}, [4]}, [5]} derived from automatic speech recognition (ASR) systems to assess phone-level and sentence-level pronunciation quality. For example, the HMM-based phone log-likelihood [1]} or log-posterior [2]}, [3]}, [4]}, [5]}. Among these methods, Goodness of Pronunciation (GOP) [2]} is widely used in pronunciation scoring task. Given an acoustic segment of phoneme with multiple frames, the corresponding GOP is defined as the normalized frame-level posterior probability over the segment.
